This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In a July 2005 paper in the Journal of Cell Biology, Mike Rout's laboratory (Rockefeller) reported the startling finding that they could isolate entire, intact SPBs on IgG-magnetic beads using Protein A-tagged Mlp2 (Niepel et al. (2005) J. Cell Biol. 170:225-235). The SPB is the yeast centrosome. The MLP2 gene and the related MLP1 gene encode filamentous proteins related to the vertebrate Tpr protein. Mlp1 and Mlp2 attach to nuclear face of nuclear pore complexes, but Mlp2 also contacts SPBs via direct binding to the core components Spc110, Spc42 and Spc29. We propose to use the ability to isolate SPBs using a tagged version of Mlp2 with an eye to identifying phosphorylation sites on SPB components. The investigators identified 11 of the 18 core SPB components by excising bands from a gel of the proteins in the SPB preparation. While this technique clearly works, it is not optimal for the identification of all of the proteins in the complex or for the identification of phosphorylated peptides. We propose to revisit the mass spectrometric analysis of Mlp2-SPBs using MuDPIT and other tactics optimized for the identification of phosphorylation sites to create a SPB phoshoproteome.